I didn't watch every single episode of it, but from what I saw I think Babylon 5 had a really good Finale.
Then unexpectedly got a season 5, but weren't sure if there would be a season 6, so ended up hedging their bets with an odd season (compared to the others).
And then the post-show movies provided a few more opportunities, but never evolved into follow-on series.
Sleeping In Light was always intended to be the finale; once season 5 got secured they shot another episode (which was also great) to act as season 4 finale.
The uncertainty with season 5 did play havoc with the pacing of the arcs. Season 4 did have to cover a lot of ground to get the most important arcs to close, so parts of it feel rushed, and vice versa the beginning of season 5 takes a while to get back to speed. Sigh.